P0731 on 2019-2020 Ram 3500: Gear 1 Incorrect Ratio & K1 Snap Ring Failure Guide

What's Unique About the 2019-2020 Ram 3500

Unlike many vehicles where P0731 can have various causes, on the 2019-2020 Ram 3500 with the Aisin AS69RC (sales code DF2) or AS66RC (sales code DF3) transmission, this code is overwhelmingly linked to a specific mechanical failure. A factory defect in transmissions built on or before December 1, 2022, causes the K1 clutch snap ring to dislodge from its groove, resulting in a complete loss of torque transfer for gears 1 through 4. Ram has issued multiple TSBs, like 21-002-23 Rev. B, and a Customer Satisfaction Notification (71A) detailing the problem and the specific repair kit required, making accurate diagnosis vital to avoid an unnecessary full transmission replacement.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light (Malfunction Indicator Lamp) is on, with DTC P0731 stored.
• Complete loss of shifting into or using gears 1, 2, 3, and 4.
• Vehicle only has 5th gear and Reverse available.
• Extremely poor or no acceleration from a complete stop (as the truck tries to start in 5th gear).
• Vehicle goes into 'limp mode' with a warning message on the dash.
• A slight shake or shudder felt just before the failure occurs, as described by some owners.

Most Likely Causes

1. Dislodged K1 Clutch Snap Ring 🔴 High Probability This is a known factory defect in Aisin AS69RC and AS66RC transmissions built on or before Dec 1, 2022, as documented in TSB 21-002-23 Rev. B. The issue is believed to be either a defective snap ring or an improperly machined groove in the K1 input shaft drum. This prompted NHTSA investigation PE24009 in March 2024 after receiving 82 initial complaints.
   How to confirm: Confirm the vehicle has an Aisin transmission (sales code DF2 or DF3) and check for the applicability of TSB 21-002-23 or Customer Satisfaction Notification 71A. The definitive symptom is the specific loss of gears 1-4 while 5th and Reverse still work, accompanied by code P0731. Final confirmation requires visual inspection during transmission disassembly.
   Typical fix: Perform the repair outlined in TSB 21-002-23, which involves removing the transmission and replacing the K1 clutch snap ring and potentially the K1 input shaft drum sub-assembly using repair kit 68637534AA. The TSB explicitly warns technicians NOT to replace the entire transmission.
   Est. part cost: $300-$800
2. Low or Contaminated Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly
   How to confirm: Check the transmission fluid level and condition. While this is a basic and necessary check for any transmission issue, it is almost never the root cause for this specific P0731 failure pattern on these trucks.
   Typical fix: If fluid is low or dirty, perform a fluid and filter change using the correct Mopar ASRC fluid and repair any leaks. However, this is extremely unlikely to resolve the code if the K1 snap ring has already failed.
   Est. part cost: $150-$250

Rare But Worth Checking

• Faulty Shift Solenoid or Valve Body: → Shop Transmission Valve Body While a possible cause on other vehicles, this is exceptionally rare for an isolated P0731 on this Ram platform. A solenoid or valve body failure would typically present with different symptoms, affect multiple gears differently, or set additional, specific solenoid-related DTCs.
• Failed Input/Output Speed Sensor: A failed speed sensor is a very rare cause for an isolated P0731 code. A bad sensor would usually trigger its own separate DTC (like P0716) and could cause erratic shifting across all gears, not just the specific 1-4 failure mode.

Diagnosis Steps

1. Use a professional scan tool to confirm P0731 is present and check for other gear ratio codes (P0732, P0733, P0734).
2. Verify the vehicle's build date and transmission type (Aisin AS69RC or AS66RC). Check your VIN against TSB 21-002-23 Rev. B and Customer Satisfaction Notification 71A.
3. Check the transmission fluid level and condition to rule out basic issues, ensuring the correct Mopar ASRC fluid is used.
4. Carefully test drive the vehicle (if possible) to confirm the classic symptoms: inability to use gears 1-4, with only 5th and Reverse functioning.
5. If the TSB applies and symptoms match, the diagnosis is a failed K1 snap ring. Do not waste time or money on replacing external parts like sensors or solenoids.
6. The repair procedure requires removing the transmission, then the torque converter and oil pump to access and replace the K1 clutch assembly components as per the TSB.

Parts You'll Likely Need

• K1 Clutch Snap Ring Repair Kit (OEM #68637534AA) — This is the official Mopar kit specified by TSB 21-002-23 to correct the known K1 snap ring failure. It includes the revised K1 clutch assembly and other necessary components for the repair.
  Trusted brands: Mopar (OEM)
  OEM price range: $300-$800
• Mopar ASRC Automatic Transmission Fluid (OEM #68224232AA) — The Aisin transmission requires this specific fluid, which is not compatible with ATF+4. The transmission must be drained for repair, requiring a full fluid replacement.
  Trusted brands: Mopar ASRC Automatic Transmission Fluid
  OEM price range: $150-$250
  Aftermarket price range: $100-$180
• Transmission Filter and Pan Gasket — Standard procedure to replace whenever the transmission is serviced or the pan is dropped.
  Trusted brands: Mopar
  OEM price range: $50-$100
  Aftermarket price range: $30-$60

Related Codes That Often Appear With This One

• P0732, P0733, P0734 — These codes for 'Gear 2/3/4 Incorrect Ratio' often appear alongside P0731 because the underlying K1 snap ring failure affects the entire clutch pack responsible for gears 1 through 4.

Technical Service Bulletins (TSBs) & Recalls

• 21-002-23 Rev. B: 'K1 Clutch Snap Ring Repair' - The primary document identifying the cause as a dislodged snap ring and outlining the repair for P0731. It applies to vehicles built on or before Dec 1, 2022.
• Customer Satisfaction Notification (CSN) 71A: A proactive campaign by Ram to replace the K1 snap ring on approximately 5,440 identified 2022 model year trucks to prevent failure.
• 21-051-24: Notes that P0731-00 will set during a key cycle and shifting into Drive on affected vehicles.
• 9100122: Explicitly advises technicians to refer to TSB 21-002-23 for P0731 and to NOT order a complete transmission.

Platform-Specific Known Issues

• A widespread defect involving the K1 clutch snap ring dislodging in Aisin AS69RC and AS66RC transmissions is the primary cause for P0731 on these trucks.
• NHTSA opened a formal investigation (PE24009) on March 27, 2024, into these snap ring failures after receiving at least 82 complaints for 2022 models alone.
• Ram issued TSB 21-002-23 (and subsequent revisions) to address this specific failure, providing a detailed repair procedure that avoids full transmission replacement.
• Ram also issued Customer Satisfaction Notification (CSN) 71A to proactively repair approximately 5,440 identified vehicles manufactured with the defective snap ring before they fail.

Mechanic-Grade Diagnostic Values

• AS69RC Small PWM Solenoid Resistance (Yellow Connector) — expected: 4 - 6 Ohms. Failure: Reading outside of this range indicates a faulty solenoid winding.
• AS69RC Large PWM Solenoid Resistance (Black Connector) — expected: 4 - 6 Ohms. Failure: Reading outside of this range indicates a faulty solenoid winding.
• AS69RC On/Off Solenoid Resistance (Green Connector) — expected: 11 - 21 Ohms. Failure: Reading outside of this range indicates a faulty solenoid winding.

Hidden / Shadow Codes Worth Checking

• P0731-00: The '-00' is an FCA/Stellantis Failure Type Code (FTC) indicating 'No Sub Type Information' or a general component failure. While not truly hidden, it is the specific variant of P0731 consistently reported in relation to the K1 snap ring failure. (see via Standard professional scan tools like wiTECH will display the code with its FTC.)

Scan Tool Commands That Help

• wiTECH or equivalent professional scanner: View Event Data — Crucial for edge-case diagnosis. Check if the P0731 fault was set while in Park/Neutral (points to possible PCM issue) or with input RPM at zero (points to possible input speed sensor issue), which could rule out the mechanical snap ring failure.
• wiTECH or equivalent professional scanner: Transmission Quick Learn / Adaptation Reset — This procedure is typically required after any major transmission repair, such as replacing the K1 clutch assembly or the entire transmission, to ensure the TCM has the correct data for clutch fill volumes and shift points.

Wiring & Ground Locations

• TCM Fuses (Under-hood Fuse Box/TIPM) — In the main fuse box under the hood, located on the driver's side in front of the battery.. Power loss to the TCM can cause various transmission codes and shifting issues. Check fuses F21, F22, F57, and F72. Depending on the specific configuration, F32 and F33 may also be involved.
• Internal Solenoid Harness — Inside the transmission, connected to the valve body and solenoids.. While rarely the cause for this specific failure pattern, knowing the wire colors can aid in bench-testing the valve body if a deeper electrical diagnosis is attempted. For example, the Yellow/White wire goes to Linear Solenoid 1.

Real Owner Repair Stories

• YouTube user 'Bobby J Farms' (2022 Ram with Aisin Transmission) — Felt a 'boom' when transmission attempted to downshift uphill. Lost gears 1-4, check engine light on.
  ❌ Tried (didn't work) The first failure at 2,600 miles was 'fixed' by replacing the entire transmission. However, the replacement transmission, which was a new unit from Mopar, failed with the exact same K1 snap ring issue a second time.
  ✅ What actually fixed it The second failure was repaired using the specific Mopar K1 clutch repair kit, part number 68637534AA, as outlined in the TSB. This suggests the kit contains revised parts not present in the earlier complete replacement transmissions.
• Reddit user 'OurRoadLessTraveled' (2022 Ram 3500 HO) — No failure occurred; the repair was done proactively by the dealer.
  ✅ What actually fixed it The dealer proactively performed the K1 snap ring TSB repair based on the vehicle's VIN being part of a Rapid Service Update (RSU). The user noted that transmission serial numbers starting with '2' followed by letters D through L were suspect, with D-H having a higher failure rate. The fix involves replacing the K1 clutch pack.

OEM Part Supersession History

• N/A (Defective K1 assembly in original transmission) → 68637534AA — This is the designated repair kit containing the revised K1 clutch assembly to permanently fix the dislodged snap ring issue per TSB 21-002-23.
  Heads up: Entire replacement transmissions manufactured before December 2022 may still contain the defective K1 snap ring assembly, as documented in owner repair stories. Using the specific repair kit is critical.

Model Year Variations Within This Range

• 2019-2021: According to TSB 21-002-23 Rev. B, the K1 snap ring TSB only applies to these model years if the vehicle had a complete NEW transmission installed between February 1, 2022, and December 18, 2022. Original transmissions on these years are not covered by this specific TSB, implying the defect was introduced in later production.